NASA's Dawn Makes History by Orbiting a Dwarf Planet

NASA’s Dawn spacecraft has achieved the distinction of becoming the first to orbit a dwarf planet. The spacecraft recently began circling Ceres, the largest known body in the main asteroid belt that sits between Mars and Jupiter.

Dawn confirmed its orbiting success by sending a signal to mission controllers at NASA’s Jet Propulsion Laboratory around 8:36 AM EST today. The spacecraft has also become the first to orbit two extraterrestrial bodies; it explored the huge asteroid Vesta—the second largest body in the main asteroid belt—from 2011 to 2012.

“Since its discovery in 1801, Ceres was known as a planet, then an asteroid and later a dwarf planet,” said Marc Rayman, Dawn chief engineer and mission director at JPL, in a press release. “Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls Ceres home.”

Ceres has undergone several classification changes ever since Sicilian astronomer Father Giuseppe Piazzi discovered the body in 1801. Researchers first labeled it as a planet and later called it an asteroid. By 2006, Ceres was finally designated a dwarf planet alongside Pluto and Eris.

Both Ceres and Vesta could have eventually developed into full-size planets if their development hadn’t been interrupted by Jupiter’s gravity. Ceres has an average diameter of 950 kilometers, whereas Vesta has an average diameter of 525 kilometers. But Vesta is a very dry body as the result of having formed earlier. Ceres consists of about 25 percent water.

"These bodies are samples of the building blocks that have formed Venus, Earth and Mars,” said Carol Raymond, Dawn deputy principal investigator at JPL, in an earlier press release. “Vesta-like bodies are believed to have contributed heavily to the core of our planet, and Ceres-like bodies may have provided our water."

The Dawn mission wouldn’t have been able to visit both Vesta and Ceres without its efficient ion engines. The three engines in the ion propulsion system ionize Xenon propellant and accelerate the ions outward to provide thrust ten times greater than that produced by chemical rockets. Dawn usually just relies on one engine at a time.

The Dawn spacecraft will stay in the shadow of Ceres until about mid-April, when it will emerge from the dark side and begin moving to lower orbits. NASA and its international partners, such as the German Aerospace Center, Max Planck Institute for Solar System Research, the Italian Space Agency and the Italian National Astrophysical Institute, should be able to look forward to much more science to come from the mission in the next year and a half.

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